The read and write head portions of the slider for use in a typical prior art magnetic disk recording system are built-up in layers using thin film processing techniques. Typically the read head is formed first, but the write head can also be fabricated first. The conventional write head is inductive and the read sensor is magnetoresistive. In the typical process of fabricating thin film magnetic transducers, a large number of transducers are formed simultaneously on a wafer. After the basic structures are formed the wafer is cut into rows or individual transducers.
The various photolithography steps involved in the fabrication of a magnetic head require precise alignment with previous structures. The photolithography masks include alignment marks for use in aligning the various patterns on the wafer. The marks may be of various types including arrays parallel lines, boxes or gratings and are located in regions of the wafer that are not being used for the heads. Typically a first mask creates a plurality of alignment marks on the wafer at a first patterning step and subsequent masks contain masks portions which are aligned to the previously formed mask. Standard photolithography equipment such as steppers have the capability of automatically detecting previously formed alignment marks. The amount of mask misalignment is a critical source of error during subsequent operations. As recording density requirements increase, the precision of alignment between the read head and the write head must also increase. Typically the read head is fabricated first. Ideally the masks used to form the write head structures should be critically aligned with the magnetic sensor structure (stripe) in the read head. The magnetic sensor layer which will also be called the K3 layer herein. The magnetic stripe must be thin, e.g. currently around 25 nm, so the alignment marks defined at the K3 layer are shallow and these marks cannot be used for alignment of subsequent layers due to the weak stepper signal generated. Therefore, current practice is to use an independent first layer (Z0 layer) for alignment which is an indirect approach which introduces an additional source of error.
What is needed is method of enhancing the shallow alignment marks created in a relatively thin layer such as the sensor layer so that subsequent layers such as write head layers can align directly to alignment marks created during the fabrication of the relatively thin layer.